Chap 10. Chain-growth Polymerization Chain-Growth Polymerization (Addition) Processes 1. Free radical Initiation Processes 2. Cationically Initiated Processes 3. Anionically Initiated Processes 4. Group Transfer Polymerization 5. Coordination Polymerization

Chain Growth Polymerization Characteristics Only growth reaction adds repeating units one at a time to the chain Monomer concentration decreases steadily throughout the reaction High Molecular weight polymer is formed at once; polymer molecular weight changes little throughout the reaction. Long reaction times give high yields but affect molecular weight little. Reaction mixture contains only monomer, high polymer, and about 10-8 part of growing chains.

Chain Growth Polymerization (ⅰ) Initiation kd : 개시제 분해속도 상수 : 10-4 ~ 10-6 L/mole sec 가열(60ºC) 자외선 kd Primary radical AIBN 결합에너지 = 46 kcal/mole P 궤도의 radical 불안정함

(ⅱ) Propagation kp : 102 ~ 104 L/mole sec

(ⅲ) termination (a) Coupling or combination(재결합)

(b) disproportionation(불균화) kt=ktc+ktd 106 ~ 108 L/mole sec

Chain Growth Polymerization Kinetic Chain Length : kinetic chain length v of a radical chain polymerization is defined as the average number of monomer molecules consumed (polymerized) per each radical, which initiates a polymer chain. ex) Monomer # 4000 Disproportionation ν=4,000/4 =1,000 Decided by step 1,2,3. Physical Chain Length : This condition contains Step 1,2,3,4 Radical 1,2,3,4

Kinetic Chain Reaction Non-Polymerization Reaction Peroxide induced Bromination of Toluene 1) Initiation Two types of reaction  R-O-O-R 2RO• (1)  R-O• + Br2 ROBr + Br• (2)  R-O• + ФCH3 ROH + ФCH2• (3) Tow radicals and tow kinetic chains formed by decomposition of each ROOR molecules

Kinetic Chain Reaction 2) Propagation  Br• + ФCH3 HBr + ФCH2 (4)  ФCH2• + Br2 ФCH2Br + Br • (5) Two special features Number of active species is fixed  During kinetic chain reaction, same reactions was repeated

Kinetic Chain Reaction 3) Termination  2 Br• Br2  2ФCH2• ФCH2 CH2Ф  ФCH2• + Br • ФCH2Br + Br • NET EFFECT OF KINETIC Chain rexn: One ROOR molecule can cause formation of Br2, CH2CH2, CH2Br,HBr, ‥.

Kinetic Chain Reaction Comparison Chain Polymerization & Chain Reaction Init. propagation termination Chain reaction Ri == Rt Reaction Rate Steady state Time Induction period In proportion to the O2 concentration

Kinetic Chain Reaction In case of Chain reaction, there are mainly induction periods, due to the inhibitor. If an active center is formed, the reaction rate accelerate and then come to steady state. The whole reaction rate is reaching plateau region. Linear Chain-Growth: Polymer of high DPn found easily in early reaction Linear Step-Growth: high extent of reaction value required to obtain high DPn

Kinetic Chain Reaction Comparison Free Radical Reaction & Ionic Reaction - Ionic Initiation – multiple bond addition, ring opening polymerization - Radical Initiation – Ring-opening polymerization has not initiation reaction.

Kinetic Chain Reaction Comparison Free Radical Reaction & Ionic Reaction

Kinetic Chain Reaction Comparison Free Radical Reaction & Termination Step of Ionic Reaction A) Free Radical Termination Two molecules involved = bimolecular reaction

Kinetic Chain Reaction B) Cationic Termination Anionic capture is analogous to combination of free radical reaction. But, this reaction can’t include increasing of MW because of unimolecular reaction

Kinetic Chain Reaction The proton release is similar to disproportion of free radical.. But, one chain join in the reaction unimolecular reaction

Surfing to the internet Kinetic Chain Reaction Surfing to the internet For further details about Chain Growth Polymerization Click next homepage. http://www.cem.msu.edu/~reusch/VirtualText/polymers.htm

Kinetic Chain Reaction Free Radical Initiated Polymerization of Unsaturated monomers Kinetic Scheme Initiation Two step sequence-Both enter into overall rate Initiator decomposition I2 2I 2. Initiator fragment 가 모노머에 첨가, Chain growth의 개시. I+M IM Initiator의 efficiency는 desired reaction과 side reaction 과의 경쟁에 의해 결정됨. kd ki Primary radical species 일반적으로, 0.5 << f << 1

Kinetic Chain Reaction A.Cage Effect –primary recombination Initiator fragments surrounded by restricting cage of solvent Ex) (acetyl peroxide)

Kinetic Chain Reaction I) Recombination possible I2 2I II) 만약 free radical 이 cage에 있는 동안 elimination reaction 이 일어나면 Radical combination으로 인해 안정한 분자 형성 Inactive Species 도 형성

Kinetic Chain Reaction B. Induced Decomposition –Secondary combination I) Radical이 peroxide 분자를 공격함으로 해서 R + R-O-O-R RH + ROOR R=O + RO 결국, R + ROOR ROR+ RO Total number of radical 은 변하지 않았으나 그중 반수의 분자들이 낭비. II) Chain Transfer to Solvent 이 경우도 한 라디칼 밖에 못 얻으므로 개시제의 반이 낭비되었다.

Kinetic Chain Reaction III) Reaction with Chain Radical 개시제 분자 모두가 중합반응 개시에 관여하지 않으므로 efficiency factor를 집어넣음. f: Initiator Efficiency = mole fraction of initiator fragments that actually initiate polymer chains. 0.5 < f < 1.0

Kinetic Chain Reaction C. Reaction Rate [M] 가 크기에 관계없이 모든 Chain radical 농도를 대표한다면 즉, M = IM or = I M f  1 Ri는 [M] 과 무관 f=[M] f < 1 Ri 는 [M]과 관련 [M] , f [I2] , f due to induced decomposition by convention, 두 radical 형성

Kinetic Chain Reaction D. Initiator 등의 결합을 가진 화합물들. Acetyl peroxide, or benzoyl peroxide 80~100C Alkyl peroxide, cumyl or t-butyl peroxide 120~140C

Kinetic Chain Reaction Hydroperoxides, cumyl or t-butyl 80~100C 50~70C AIBN 2,2 azobisisobutyronitrile

Kinetic Chain Reaction Propagation Termination By convention 2개의 라디칼이 소멸되므로

Kinetic Chain Reaction Overall Rate of Polymerzation Radical concentration 측정하기 어려움, 농도가 작다. (~10-8molar) 따라서 이 term을 이용하는 것이 비현실적. [M]을 제거하는 것이 바람직. (# of propagation step >>> # of initiation step)

Kinetic Chain Reaction [M]을 제거하는 방법 Steady-State Assumption 라디칼 농도가 처음에 증가하고 동시에 constant한 정상상태에 도달한다. 그리고는 reaction rate change가 0이 됨. (active centers created and destroyed at the same time) Ri = Rt ※중합속도식 1/2승 법칙

Kinetic Chain Reaction f<1인 대부분의 system에서 [I2]1/2가 맞음. (square root dependence of [I2]) ※ Odian Fig. 3-4 MMA using BPO Vinyl Acetate using AIBN AIBN Rp [I2]1/2 BPO -CO2 2 300C + N2 Azobisisobutyronitrile

Kinetic Chain Reaction f < 1인 경우에 SRD 가 맞지 않는 경우 왜냐하면 f 가 [M] 에 ‘dependent’. Why? Due to induced decomposition of toluene + [I2]

Kinetic Chain Length (KCL) At S-S assumption (1) Disproportionation의 경우 Knowing that (2) Coupling or combination의 경우

Kinetic Chain Length (KCL) (3) 모두 일어날 경우

Kinetic Chain Length (KCL) Degree of Polymerization (중합도) 중합도 DP 는 모노머 농도가 증가할수록 개시제 농도가 감소할수록 (1) Dispropotionation의 경우 (2) Coupling의 경우

Kinetic Chain Length (KCL) (3) 둘 모두 일어날 경우

Kinetic Chain Length (KCL) (1),(2),(3)식으로부터 만약 Chain transfer가 없고 S-S assumption이 valid한 경우 개시제 효과 (2),(4) 식으로 알 수 있다. 이 valid 한 경우 ,

Chain Transfer M + XY MX + Y Chain transfer agent Chain transfer 가 있더라도 Rp는 변하지 않으나 DPn에는 영향을 미침. (왜냐면 Rp=kp[M][M] 대신 [Y]이므로) ex) (1) 용매나 첨가제에 의해 chain transfer agent로transfer가 일어남. 이 경우 chain transfer coefficient가 높음. (2) 모노머나 고분자로 transfer가 일어난 경우 등.

Chain Transfer Inhibitor and Retarder Inhibitor (방지제) Y이 사슬 중합의 개시반응에 참여할 수 없을 때. 고분자를 한 장소에서 다른 장소로 옮길 때, hydroquinone등. Retarder (지연제) Y이 반응성이 낮을 때, 이 두 물질들이 모노머에 포함되어 MW조절용으로 mercaptan등 중합방지용으로 쓰임. - 이 같이 chain transfer가 일어날 경우

Surfing to the internet Chain Transfer 그래프의 기울기로부터 chain transfer codfficient ‘Cs’를 구한다. See Odian P.235 1 Surfing to the internet For further details Click next homepage. http://www.chem.rochester.edu/~chem421/ct1.htm DPn [5]/[M]

Temperature Dependence of Rp and DPn Assume : no chain transfer

Temperature Dependence of Rp and DPn slope of lnRp/T is ( + ) as T  lnRp  but Rate of Increase  as d lnRp/dT 

Temperature Dependence of Rp and DPn

Ceiling Temperature Polymer-Depolymerization Equilibria 중합의 생장 반응 해중합이 고려되는 화학평형이 생김 ΔGp = ΔHp – TΔSp ΔHp : 중합열 ΔSp : monomer 와 polymer의 분자 배열의 차 At eq. State ΔGp=0 어느 온도에서 중합반응이 평형에 도달, 그 온도 이상에서는 중합이 진행하지 않는 온도 ceiling Temperature(Tc)

해중합이 두드러지는 온도에서 중합 반응 속도식 라면, M Tc

Ceiling Temperature Polymer-Depolymerization Equilibria k sec-1 kdp Tc :이 온도 이상에서 반응이 일어나지 않는다. 이 온도 이하에서 안정 kp[M] kp[M]- kdp 300 400 500 Tc

Ceiling Temperature Polymer-Depolymerization Equilibria ※Odian Fig 3-18 Entropy changes for all polymers are not so different. Sp= Sp- Sm Sp가 더큰 (–) value를 가짐. Hp= Hp- Hm (–) 이면 exothermic.

Trommsdorff Effect or Gel Effect Polymer 말단의 radical 운동이 부자유(정지반응이 큰 영향을 받음) kp는 [M]의 감소에 비례해서 감소하지 않고 오히려 증가 ( ∵ kp는 반응진행에 따라 변하지 않으나 kt는 반응진행에 따라 차츰 작아지므로) 이러한 효과를 자동 촉진 효과 (autoaccerelation effect) Polymer 농도가 증가하면 계의 점도가 증가

Trommsdorff Effect or Gel Effect  one would expect ξ  as t  그러나 ξ  as [M0]  80% 60%  autoacceleratioan 40% as [M0] drastic in . 10% t