理學(xué)《聚合反應(yīng)原理專論》 chapter中科大研究生教學(xué)課件

1、Chapter 2 Controlled free radical polymerization 2-1 The significances of living free radical polymerization 1. Importance in polymer industry (1) Most of polymer materials are produced by the method of free radical polymerization u Process conditions: bulk, solution, suspension, emulsion polymeriza

2、tions. u Medium: water and common organic compounds (2) The needs of controlling molecular weight u Big effects of MW and MWD on the properties of polymer materials. For example, the MW of poly(acrylonitrile） used in making fiber is around 5 x104, also narrower molecular weight distribution is neces

3、sary. (3) The need of controlled polymer structure u Effect of compositions and structure on the properties of materials The structure of ABS resin is (AN)x(Butadiende)y(styrene)z. It has excellent physical properties in comparison with PSt. (4) Developing new products u Products from homopolymeriza

4、tion are limited. u The synthesis of new monomers is very difficult. u Copolymerization can produce a varity of new polymer materials. u No organic solvent coatings. 2. Development of polymerization theory u Control activity of free radical u Polymerization kinetics u The synthesis of complicated st

5、ructure is possible. 2-2 Difference between anionic and free radical polymerization Table 2-1. Comparison of free radical with living anionic polymerization Active Species Initiation rate (mole/sec) Conc of active species (mol.L-1) kapp (L/mol- sec) kt (L/mol-s) s (Sec) AnionicVery fast 10-4 10-2 2

6、3800smallLong Free radical 10-10 10-810-9 10-7 102 104106108 0.1 10 2-3 Progress of living free radical polymerization 1. Living polymerization system containing Cr+ and peroxides (1) Ageing C OO C OO + Cr +2 C O OC O -O + Cr +3. + 3 Cr + C O -O. C O O (2) Initiation and propagation reactions 3 Cr +

7、C O -O. C O O MMA C O O CH2 C C=O OCH3 CH3 C O -O Cr + 3 . Propagation reaction C O OC O -O Cr +3. CH2 C OCH3 C=O CH3 n CH2 C OCH3 C=O CH3 CH2 C OCH3 C=O CH3 n+1 CH2 C OCH3 C=O CH3 .3 Cr + C O -O C O O MMA Free radical has faster initiation and polymerization rates comparison with free radical pair.

8、 (3) Initiation efficiency u R group has big effect on the activity of radical pair, steric hindrance of the group is a key factor. COOC OO C O O O C O O O R=O R= Initiation efficiency ( f ) = number of radical residues in the polymer/ number of radicals produced R O OO O R Ketopinyl peroxide (過氧化茨烷

9、酮酰過氧化茨烷酮酰) The effect of polymerization temperature 0510152025 0 10 20 30 f (%) Temperature ( oC) The influence of temperature on the f value BPO KPO COOC OO C O O O C O O O 2. Initiation system by thermal decomposition (1) The compounds with triphenyl methyl group Ph3CCH2CH2CH2OH N N CPh3 C CC Theo

10、retical consideration Homolytical split of C-C bond in polymerization condition Triphenyl methyl radicals are very stable and can exist in high concentration CC CPh3CPh3 Fast equilibrium, reduce the concentration of chain radicals CH2CH CPh3 CH2CH CPh3 The reaction of free radicals Ph3C CHPh2Ph3C +

11、. CHPh2 . heat Ph3C . . O2, ROH fast Ph3COOH Ph2CH O2, ROH fast Ph2CHOOH Ph2CH. Ph2CH CHPh2 The experiment evidence Structural analysis The polymerization initiated by hexaphenyl ethane CPh3Ph3C MA Ph3C (MA)nCPh3 n2 3 When initiation of MA, no good result was obtained with triphenylethane, probably

12、due to slow initiation. Initiation reaction Ph NN CPh3PhN2CPh3 Ph CH2CHPh CH2CH Ph NN CPh3 Thus azo compounds were synthesized Initiation and polymerization mechanism Ph N=N CPh3 heat Ph + CPh3 . . . . . Ph + CH2=CH Ph CH2CH Initiation Propagation CH2CHCH2 CHPh . ( )nCH2=CH+ n ( )Ph CH2CHCH2CH. +1 +

13、 n ( )Ph CH2CHCH2 CH. CPh3 n ( )Ph CH2CHCH2 CH CPh3 Some side reactions Ph N=N CPh3 Benzene heat N2 + Ph + Ph3C . . Ph + Ph H . 1 1 . Ph3C+ Ph H H CPh3 2 . Ph H +Ph3C.Ph3CHPh+ Another compounds as initiator C Radical polymerization of MMA, St, and MA C CPh3 CH3 COOCH3 C CH3 COOCH3 . + CPh3 . . . C C

14、Ph3 H COOCH3 CH CPh3 CH .CPh3 .CPh3 + C H COOCH3 + StericStable of benzyl radical Livin g Normal Oligomer (2) Other thermal decomposition initiators a. Dibenzyl radicals +M CC X X C X (M)nC X X = CN, C2H5, OC6H5, OSi(CH3)3 Typical example is: CC Ph CNCO OCH 3 CH 3 CH 3 Ph C CO OCH 3 CH 3 CH 3 C Ph C

15、N Ph+ . +M . C CO OCH 3 CH 3 CH 3 (M M A)n-1M M A.C Ph CN Ph + C Ph CN PhM M A n-1 C CO OCH 3 CH 3 CH 3 (M M A) +St C CO OCH 3 CH 3 CH 3 (M M A)n(St)C Ph CN Ph m b. B-O radical Borinate radical can be produced by heating, for example: Partially control polymerization of MMA C8H17O O B heat C8H17OO B

16、 . . + c. Triazolinyl radical . N N N R heat .N N N R+ +nM R (M)M. n-1 . N N N + N N N (M)R n Controllable radical polymerization of MMA, St, MA and Vinyl acetate Preparation of block copolymers Comparing two radicals N N N .N N N a b Radical stability b a 4. Design of initiator The component of ini

17、tiator: R1-C(R2)3 The bond between R1 and C(R2)3 can be C-C, C-O, C-S etc The bond between R1 and C(R2)3 should be week and can be split homolytically in the polymerization condition C(R2)3 should be stable radicals, Can exist in high concentration. Stable during the polymerization, no substitution

18、reaction, or dehydrogenation, for example, Ph3C.+. Ph3C Ph3C H C Ph Ph Ph3CC Ph Ph H The following radical can be used C Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl .C C C C F CF3 CF3 F CF3CF3 F CF3 CF3 . (5) Consider the activity match of two radicals R1 and C(R2)3 The following initiator is not g

19、ood Free radical 1 disappears and radical 2 will be accumulated in high concentration, so polymerization rate will decrease. OTe O heat O O Te . + . + CO2 1 2 5. The problems should be solved (1) Most of initiators can decompose easily, after polymerization, the end chain with stable radical can not

20、 be split easily N=N X X=S, NH heat . +X . +M (St) X n Block copolymerization can not undergo, because too strong bond is formed. (2) The polymerization is performed at higher temperature a. Thermal polymerization of monomer b. Termination will accelerate c.Side reaction due to high temperature C R1

21、 R2 PhH+CH2C CH 2 COOCH 3 +. C R1 R2 PhCH2C CH 3 COOCH 3 R1=Ph, R 2=Ph or CN (3) Loss of chain radical activity due to termination reaction +. C R1 R2 PhCH2C CH3 COOCH3 C R1 R2 PhCH2C CH3 COOCH3 R1=Ph, R2=Ph or CN These initiators are not easily synthesized. Another example: Ph3C2 . Ph3C H C Ph Ph P

22、h3C.+ R. . Ph3C H R H RCH Ph Ph + Ph Summary for the living initiating system 1. BPO + Cr2+ 1. Ph3C-CPh3, Living polymerization for MMA, normal polymerization for St, obtained oligomer for MA 3. B-O radical C8H17O O B 4. Triazolinyl radical N N N .N N N a b OTe O heat O O Te . + . + CO2 1 2 5. Te co

23、mpounds 2-3. Photochemical initiators 1. The concept of iniferter Initiator- transfer agent- terminator The compounds acts as initiator, transfer agent and terminator during the polymerization is referred as iniferter For example: The mechanism of photoinitiated polymerization in the presence of ini

24、ferter R2N C S S S C NR2 S hv R2N C S S S C NR2 S . 2 . R2N CS S +MR2N C SM S . 12 3 . R2N C S (M) S M n-1 n-1 R2N C S (M) S M. 4 +. + R2N C S (M) S n . R2N C S (M) S M n-1 R2N C S S S C NR2 S n S NR2CS+ R2N CS S . (n-1)M R2N C S (M) S S NR2CS Initiator decomposition Initiation, propagation Terminat

25、ion reaction Chain transfer reaction The experimental evidence a Compound 1 (g) Yield (%) Mn b X 104 S c (%) N d 1.00203.300.402.2 0.15251.600.781.7 0.20321.200.781.5 0.25380.960.742.2 a.10 mL of St, 27 h (St) ; b.b. Determined by viscometry; c.c. Determined by carius method; d.d. Number of (C2H5)NC

26、(S)- end groups per polymer chain measured based on S% Examples in the block copolymerization ABA block copolymers are precisely prepared, but ABA block copolymers with a narrow MWD are not obtained. R2N C S S . CH2 . S C NR2 S CH2+ +nM1 +nM1 S C NR2 S CH2(M1)R2N C S S (M1) CH2 n n +mM2 n n R2N C S

27、S (M2) (M1) CH2CH2(M1) (M2) S C NR2 S m m Preparation of A-B-A triblock copolymer Preparation of star polymers CH2SR CH2SRRSCH2 RSCH2 R= C S NEt2 hv CH2 CH2SRRSCH2 RSCH2 SR . . + a. When St was used in the polymerization, only benzene-insoluble polymer was formed due to mutual termination, so add mo

28、re R2N- C(S)S2 will decrease the benzene-insoluble polymer b. When MMA was used, it will give benzene-soluble polymer containing more than 24% star polymers with more than three functionalities. This polymer can be used as macroinitiator +. . SR CH2 CH2SRRSCH2 RSCH2 hv C S NEt2R= CH2SR CH2SRRSCH2 RS

29、CH2 MMA CH2 (MMA) CH2CH2 CH2 SR (MMA) SR (MMA) (MMA) RS RS n n n n St n nn n CH2 (MMA) CH2CH2 CH2 (MMA) (MMA) (MMA) (St) (St) RS RS (St) (St) SR SR m mm m Crosslinked polymer c. MA + Et2N-C(S)S2 + iniferter benzene-soluble star polymer Comb-like or graft polymer a. Monomer iniferter b. Thermal and p

30、hotochemical initiations CH2CH C O SC S NEt2 CH2CH CH2S C S NEt2 CH2C CH3 COCH2CH2S O C S NEt2 UV initiation polymerization Low-MW benzene-soluble polymer and a small amount of crosslinked polymer. It can be used as macroinitiator to prepare graft or comb-like copolymers. CH=CH2 CH2 S C S NEt2 CH2=C

31、HCH2(St) S C S NEt2 UV n benzene St+ CH=CH2 CH2 S C S NEt2 +MMA benzene n UV CH2=CHCH2(CH2 C) S C S NEt2 CH3 COOCH3 the first step gives benzene-soluble polymer The second step gives graft and cross-linked polymer. When A in the feed decreases, the yield of soluble graft polymer increases CH=CH2 CH2

32、 S C S NEt2 + St + AIBN benzene heat CH2CH CH2CH CH2S C S NEt2 hv CH2CH CH2CH CH2(MMA) S C S NEt2 MMA n A Surface modification The surface modification of PVC CH 2 CH CH 2 CH ClCl + NaS C S NEt2 DMF CH 2 CH CH 2 CH ClS C S NEt2 The polymer contains 15 w% of Et2N-C(S)S group. It can initiates the pol

33、ymerization of hydrophilic monomers, such as CH2CH COO CH2CH2OH 2. Type of iniferter . S C NR2 S S C NR2 S CH3 hv CH3 + . S C NR2 S CH2 hv CH2.+S C NR2 S . For example A BAB A (M) B n + .hv +nM a. Two types: AB The disadvantages a. Formation of two slightly stable free radicals; no very stable radic

34、als, no active radical b. Reactivity changes during the initiation and polymerization For example R2N C S S S C NR2 S hv R2N C S S . 2 BB BBBMB n b. hv + nM . R2N C S hv R2N C S S R2N C S S CH2CH2CH2CH2S . + R2N C S S CH2 hv . +.CH2 R2N C S (M) S CH2CH2 n n CH2R2N C S S (M) 2 . R2N C S S hv R2N C S

35、S S C NR2 S R2N C S S CH2 CH CH2CHCH2CHS C S NR2 +nM ( )n-2 bond break bond break Bond break Model reaction 1 Model reaction 2 hv, 310 nm SOC2H5 S O S OC2H5 S SOC2H5 S SOC2H5 S hv, 350 nm SOC2H5 S J. Am. Chem Soc. 1999, 121(28), 6599-6606 Selective bond breaking 3. Design of iniferter (1) Structure

36、of iniferter A-B type, the typical is R S SCR 2 N ab Broken at b to form radicals R and R2N-C(S)S, broken at a to form radicals R-S and R2N-C(S) (2) Structure of R a. R radical is not so active, R S SCR2N R=CH2 , CH2=CH C O , CH3CH COOCH3 CH3CH CN . . , If R is active, such as following example CH2C

37、H2 S SCR2N. hv Breaking S CR2N CH2CH2S.+ For example b. Consideration of R2NCS S . C S S CH2 C S S CH2 hv It is better to select more stable radical than R2NCS S . 4. Other iniferters (1) Photochemical reaction of dimethylnitrosamine Me N Me N O hv Me N Me N O. .+ (1 Torr +100 Torr N 2) The system i

38、s irradiated for 20 h, 99.9% of dimethylnitrosamine can be recovered. No self-termination by coupling and disproportionation. No self-termination for stable radical NO +NOCl hv + NOCl+ . . + NO . + HCl NO NOH The concept of self-termination and cross-termination Can we use NO. in the living free rad

39、ical polymerization? Cl.2Cl2 self terminationcross termination Cl . +NO.NOCl Thermal radical polymerization R O N 100 C o . R+O N + M RM . O N + nM O N +RM . R (M) O N n . a. Active alkyl radical and stable nitroxide radical b. Dormant species is a C-O-N bond c.Living radical polymerization of St wa

40、s developed by Georges et al in 1993 N O 2,2,6,6-Tetramethyl-1- piperidinoxyl, TEMPO 5. Feature of living radical polymerization with iniferters (1) Iniferter compounds are easily prepared and purified. (2)The MW of the polymers increases with the increase of polymerization time. (3) The first-order

41、 kinetics (4)The block copolymers are synthesized with polymers as macroinitiator. (5)The number of iniferter fragments bonded to the polymer end is independent of reaction time (6) RS group has max = 282 nm ; value =10,500, Polymerization rate of tetrafunctional and two functional iniferters are 4

42、times and 2 times than that of monofunctional iniferter. 6. Disadvantages for iniferter (1) Broad MWD up to 2 B radical can initiate the polymerization of monomer CH2CH B X CH2CH X + B . . nCH2=CHX (CH2CH) X CH2CH B X nn (CH2CH) X CH2CH X . .B + Another reason is: Considerable amount of light will b

43、e absorbed by the monomer leading to uncontrolled polymerization and side reactions Improved method is: CH2=CH COCl K+-S C OC2H5 S + CH2=CHC SC OC2H5 OS polymerization double bond initiator photodissociate bond MAX, O-ethyl xanthate Photo-polymerization of MMA and styrene S OEt SO hv 350 nm O S OEt

44、S . . + O OCH3 O OEt O OEt OS OEt S ( ) . . S OEt S O . ( ) O n-1 O S OEt O OEt S ( ) n n-1 . O S OEt C S O OEt O OEt O Table2-2 Results of the photopolymerization of MMA in benzene using MAX as photoinitiator under 350 nm irradiation at 32oC Time (min) Conversion (%) Rp x104 (g s-1) Mn X104 Mw/Mn 1

45、054.52.11.4 1584.52.11.3 20114.62.21.4 25134.52.01.3 30154.41.91.2 40164.51.81.3 a. MMA=5 M; MAX= 5 x10-3 M The polymer can be as macroinitiator for block copolymerization of MA Table 2-3 Block copolymerization of MA (5M in benzene using macro-initiator (Mn=16000, 5 mg/mL under 300 nm irradiation at

46、 32oC Time (min) Yield (%) Mn x 10-4 Mw/Mn 3053.92.1 60128.81.9 9025211.2 Photopolymerization of St St M MAX M Time (h) Yield (%) Mn 10-4 Mw/Mn Bulk5 x 10-20.521.91.4 Bulk5 x 10-21.062.91.7 Bulk5 x 10-21.5103.72.3 Bulk5 x 10-22.0125.63.4 Bulk1 x 10-14.029Gel 4.54.5 x 10-11.041.31.1 4.54.5 x 10-14.01

47、51.71.2 4.54.5 x 10-17.0292.51.6 in benzene The photo-polymerization of St proceeds not via iniferter mechanism Reasons: Iniferter method is operational only at 300 nm, this operated at 350 nm. The end thiocarbonyl thinyl group is not photo dissociable, hence reversible addition of monomers is not p

48、ossible PhCH2S C S OEt hv, 350 nm no polymerization linear PSt, narrow polydispersity no branching no molecular weight increase O OEt S CPhC S photoactive at 350 nm When compound 1 was used in the polymerization system in initiator amount, it acts as initiator, linear PSt was produced S OEt S O hv 3

49、50 nm O S OEt S . . + O . + CH2=CH O CH2CH S OEt S n 1 When more compound 1 was used, the high branched polymer was produced S OEt S O St, 350 nm CH2CHCH2CH C S C OEt OS St, 350 nm Hyperbranched polymers CH2CHCH2CH C OCH2 CH CO Selective polymerization S OEt S O hv + S OEt S St, 350 nm Graft polymer

50、s 310nm S OEt S CH2 + CH2CH2CHCH2CH CSCOEt O S CH2=CH n hv (2) Limitation of monomers, St and MMA and their derivatives can be easily polymerized with a living radical mechanism, VAc and MA are polymerized with a low or no living nature. (3) Limitation of MW, more than 30 of St monomers seem to inse

51、rt to form polymer every dissociation of C-B bond How to prepare the block copolymer with narrow polydispersity? H2NCHCOOH R1 H2NCHCOOH R2 H2NCHCNHCHCOOH R1 O R1 H2NCHCNHCHCOOH R1 O R2 H2NCHCNHCHCOOH O R2 R2 Purification is troublesome in the preparation of polypeptide 7. Solid-phase block copolymer

52、 synthesis In 1963, Merrifield reported solid-phase synthesis with a reagent attached to the polymer supports CH2CH OC NO2 CH NH R1O NO2 P deprotection group CH2CH OC NO2 CH NH2 R1O NO2 XCCHNH O R2 P CH2CH OC NO2 CH NH R1O NO2 PCCHNH O R2 deprotection group OH- PCCHNH O R2 OC CH NH R1O Polymer suppo

53、rts CH2CH OH NO2 NO2 CH2CH CH2OH CH2CH CH2C Cl O CH2CH OCH2CHCH2 OHOH CH2CH O CH CH2OH CH2OH CH2CH C Cl n PSGCH2O C CH2Cl O NaSR CH2O C CH2 O SRPSG nM1 PSG CH2O C CH2 O (M1) SR mM2 wash with solvent CH2O C CH2 O (M1) (M2) SRPSG nm R=C(S)-NR2 hydrolysis mn PSG CH2OHC CH2 O (M1) (M2) SRHO+ Solid phase

54、 block copolymer synthesis Block copolymers were prepared in good yield: Diblock copolymer: PSt-b-PMMA; Triblock copolymers: PSt-b-PMMA-b-PMMA; PSt-b-PMMA-b-PClSt; Tetrablock copolymers: PSt-b-PMMA-b-PSt-b-PMMA; PSt-b-PMMA-b-PEMA-b-PMOSt; ClSt= Chlorostyrene, EMA=ethyl methacrylate, MOSt= p-methoxystyrene The features of Radical polymerization initiated by iniferters 1. What is the