Qhov Tseem Ceeb Qhov txawv - Anionic vs Cationic Polymerization
Anionic polymerization thiab cationic polymerization yog ob hom saw loj hlob polymerization cov tshuaj tiv thaiv uas yog siv los ua ke ntau hom polymers. Ob qho kev tawm tsam no muaj tib lub tswv yim sib txawv, tab sis cov tshuaj tiv thaiv pib sib txawv. Anionic polymerization cov tshuaj tiv thaiv yog pib los ntawm ib hom active anionic, whereas cov tshuaj tiv thaiv cationic polymerization yog pib los ntawm ib hom cationic active. Qhov no yog qhov sib txawv tseem ceeb ntawm anionic thiab cationic polymerization. Ob qho tib si cov tshuaj tiv thaiv polymerization yog rhiab rau cov kuab tshuaj siv.
Anionic Polymerization yog dab tsi?
Anionic polymerization yog cov tshuaj tiv thaiv kev loj hlob uas pib los ntawm anion. Muaj ntau ntau hom kev pib siv rau hauv anionic polymerization. Cov kev tshwm sim no tshwm sim nyob rau hauv peb kauj ruam: pib, chain propagation, thiab chain termination. Cov tshuaj tiv thaiv polymerization no yog pib los ntawm nucleophilic ntxiv rau ob daim ntawv cog lus ntawm monomer. Yog li, tus pib siv rau hauv cov tshuaj tiv thaiv yuav tsum yog nucleophile.
Kev pib los ntawm kev muaj zog anion
YCationic Polymerization yog dab tsi?
Cationic polymerization tuaj yeem suav tias yog lwm pawg ntawm cov saw loj hlob polymerization cov tshuaj tiv thaiv. Ib qho cation pib cov tshuaj tiv thaiv no los ntawm kev hloov nws cov nqi mus rau ib qho monomer, uas tom qab ntawd ua rau tsim cov kab mob ntau dua. Tom ntej no, lub reactive monomer reacts zoo ib yam li lwm cov monomers los ua ib tug polymer. Tsuas muaj tsawg tus monomers uas tuaj yeem pab txhawb cov cationic polymerization saw cov tshuaj tiv thaiv. Olefins uas muaj cov khoom siv hluav taws xob pub dawb thiab cov heterocycles yog qhov tsim nyog rau cov kev tawm tsam no.
pib los ntawm protic acids
Qhov txawv ntawm Anionic thiab Cationic Polymerization yog dab tsi?
Piv txwv ntawm Cov Thawj Coj thiab Monomers:
Monomers:
Anionic Polymerization: Anionic polymerization tshwm sim nrog cov monomers uas muaj electron rho tawm pawg xws li nitrile, carboxyl, phenyl, thiab vinyl.
Cationic Polymerization: Alkenes muaj alkoxy, phenyl, vinyl thiab 1, 1-dialkyl substituents yog qee qhov piv txwv ntawm monomers siv hauv cationic polymerization.
Initiators:
Anionic Polymerization: Nucleophiles xws li hydroxide, alkoxide, cyanide lossis carbanion tuaj yeem ua tus thawj coj hauv anionic polymerization. Cov carbanion tuaj yeem tsim los ntawm cov kab mob organometallic xws li alkyl lithium lossis Grignard reagent.
Cationic Polymerization: Electrophilic agents xws li halohydric acids (HCl, HBr, H2SO4, HClO 4) yog ib pab pawg neeg pib siv hauv cov tshuaj tiv thaiv cationic polymerization. Tsis tas li ntawd, lewis acids (electron acceptors) thiab cov tebchaw muaj peev xwm tsim carbonium ions tuaj yeem pib ua polymerization. Piv txwv ntawm Lewis acids yog AlCl3, SnCl4, BF3, TiCl 4, AgClO4, thiab I2 Txawm li cas los xij, lewis acids xav tau kev sib koom tes xws li H 2O lossis cov organic halogen compound.
Mechanism:
Anionic Polymerization: Anionic polymerization xav tau tus thawj coj los pib cov tshuaj tiv thaiv thiab monomer los tsim cov polymer. Nyob rau hauv cov ntaub ntawv no, ib tug reactive anionic hom pib cov tshuaj tiv thaiv los ntawm reacting nrog ib tug monomer. Qhov tshwm sim monomer yog carbanion, uas tom qab ntawd rov ua dua nrog lwm tus monomer los tsim cov carbanion tshiab. Cov tshuaj tiv thaiv tshwm sim los ntawm kev ntxiv ib qho monomer rau cov saw loj loj tib yam, thiab qhov no ua rau cov saw hlau polymer. Qhov no hu ua "chain propagation."
Cationic Polymerization: Ib hom reactive cationic pib cov tshuaj tiv thaiv los ntawm kev khi thiab xa nws cov nqi mus rau ib lub monomer. Cov tshwm sim reactive monomer ces reacts nrog lwm monomer los ua ib tug polymer nyob rau hauv tib txoj kev raws li nyob rau hauv anionic polymerization.
Reaction Rate:
Anionic Polymerization: Tus nqi ntawm cov tshuaj tiv thaiv anionic polymerization kuj qeeb dua li cov tshuaj tiv thaiv cationic polymerization vim tias cov nqi tsis zoo ntawm tus pib anionic tuaj yeem ruaj khov los ntawm ntau lwm yam. Thaum cov ions ruaj khov, lawv yuav ua tsis tshua muaj zog.
Cationic Polymerization: Tus nqi ntawm cov tshuaj tiv thaiv cationic polymerization yog qhov nrawm dua li cov tshuaj tiv thaiv anionic polymerization vim hais tias cov cationic pib yog heev reactive, nyuaj rau tswj thiab stabilize.
Daim ntawv thov:
Anionic Polymerization: Anionic polymerization yog siv los tsim qee cov ntaub ntawv tseem ceeb xws li polydiene hluavtaws roj hmab, tshuaj styrene / butadiene rubbers (SBR), thiab styrenic thermoplastic elastomers.
Cationic Polymerization: Cationic polymerization yog siv hauv kev tsim cov polyisobutylene (siv hauv cov raj sab hauv) thiab poly (N-vinylcarbazole) (PVK).
