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Title: Synthesis of pH responsive aggregates of hyperbranched copolymer of 

cetyltrimethylammonium functionalized poly (l,2,3 triazoacrylate) and poly (acrylic acid)

ntroduction

In many applications, hyperbranched polymers (HBPs) have replaced dendrimers (which are

difficult to produce and thus expensive) and conventional polymers (which lack many useful

 properties). HBPs feature hih solubility in various solvents, low solution viscosities, hih

deree of functionality with more void space for encapsulation of macromolecules. !ill date,

synthesis of HBPs from a multifunctional core material by polycondensation method is well

followed. However, much of the startin monomers for polycondensation processes are very

expensive and hence are not encouraed in commercial applications. "uch cheaper free radical

techni#ues ($%P) may produce hihly branched polymers if a balanced combination of a

 branchin aent and a chain transfer aent is used where elation is prevented. However, HBPs

 produced by $%P lack hih deree of functionality which aain restricts their applications in

many areas. In this reard, we tried to synthesi&e a pH responsive lon alkyl chained tria&ole

functionali&ed HBP and characteri&ed its solution properties so that it could be further used for 

host'uest application.

!"perimental #etails $ #iscussions

In the first step, a branched copolymer of proparyl acrylate (P) and acrylic acid () was

 prepared by $%P in presence of varied concentration of a branchin aent (divinyl ben&ene'*B) and a chain transfer aent (dodecane thiol'!). !ypically, measured #uantity of P,

*B and ! were dissolved in "$. !hen and $%P initiator (IB+) were added to the

resultant mixture and homoeni&ed for - minutes under nitroen blanket. $inally,

 polymeri&ation was carried out at -/0 for 1- hrs (optimi&ed condition which prevented elation

and yielded maximum products). !he final polymer masses were precipitated from water and

collected after centrifuation at 2--- r.p.m. !he settled masses were free&e dried. In order to

remove other unreacted inredients, the masses were further precipitated from diethyl ether and

vacuum dried. 3H+"% (d4'"56) 7 (ppm)8 3.9'3.4 ('0H1 of polymer backbone), 1.9 ("56

and H0:0' of proparyl moiety), 9.9 ('0H1 of pendant unreacted vinyl roups derived from

*B residues where only one vinyl roup has underone polymeri&ation, i.e. actin as

 branchin unit), '.9 (aromatic hydroens in *B) and 31'3 ('066H). $!I% ; (cm '3)8 1<=

(:0H stretchin), 1313 ('0:0' stretchin), 1<29 > 1=19 (symmetric > asymmetric stretchin of 

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 ?0H1), 3- (0@6 of ester stretchin) and 342- ('066H stretchin). In our study, we used

various compositions of startin materials to synthesi&e HBPs like P39-A9-A-A- (P'9- mmol, '9-

mmol, *B'- mmol > !'- mmol), P39-A9-A3.19A1.9, P39-A9-A1.9A1.9, P39-A9-A9.-A1.9, P3-A-A1.9A1.9  and

P3-A-A1.9A1.9. ll P3'HBPs (-.3 Aml) except P39-A9-A-A- were soluble in 0H0l, "$, 0", '0H,

t'Bu6H, acetone, "56 and alkaline medium. !hey exhibited low solution viscosities in "$

in the rane -.2'-.= dlA unlike 2.2 dlA of the linear analoue. Interestinly, CP0

characteri&ation revealed HBPs had hih "nav in the rane x3-4 Amol unlike 2x3-4 Amol of 

the linear analoue. CP0 also confirmed hyper branchin in all samples as they had broad PI

(<'3-) and low values of D (E -.9'-.4). In the next step, we attempted to prepare pH responsive

areates from P3'HBPs. P3'HBPs contained free proparyl roups and thus could be used for 

click reactions' a potential tool for functionali&ation.

Fe prepared cetyltrimethylammonium a&ide (0!+) from 0!B by a simple 5+1 reaction with

 +a+ in "$ at =-/0 for 12 hrs. 0!+  is soluble in "$ and thus was isolated by ultra

filtration where +a+ and 0!B precipitated out. !he orane filtrate was precipitated to diethyl

ether and vacuum dried at 9-/0 for an overniht. 3H+"% (d4'"56) 7 (ppm)8 1.9 ("56) >

.2 ('0H1 +). $!I% ; (cm'3)8 1=39 > 1<29 (asymmetric > symmetric stretchin of ?0H 1 from

0! roup), 1-== (0'+ stretchin). G5I mass mA&8 1<2 "J.

$inally alkyne rich P3'HBPs were functionali&ed with 0!+. In a typical process, P3'HBPs

and 0!+  were dissolved in 38 3 t'Bu6H8 H 16 medium. !hen 0u562.9H16 and sodium

ascorbate (+asc) were added to the mixture and pured under nitroen for - minutes. 0lick 

reaction was carried out at 4-/0 for 2< hrs (click reaction on polymer is a slow process). !hen

these functionali&ed HBPs (P1'HBPs) were isolated by centrifuation at 2--- r.p.m for 39

minutes and dialy&ed aainst G! solution continuously for 1 days and then aainst . H16

for another 1 days. $inally the samples were free&e dried and rounded to fine reen powder.

$!I% ; (cm'3)8 3143 (+'+ stretchin of 3, 1, tria&ole moiety). !here was no characteristic $!I% 

 peak of alkyne or a&ide moieties in P1'HBPs. P1'HBPs (-.3 Aml) were soluble only in "$,

"56 and alkaline medium. Kimited solubility of P1'HBPs in various solvents miht be due to

their functionali&ation with lon alkyl chained tria&oles. P1'HBPs underwent pH dependant

reversible self assemblin. ll samples of P1'HBPs except P19-A9-A-A- showed a sharp Lump in

hydrodynamic diameter (h) from 3-1  to 3- nm and in &eta potential value from '- to 3-

m5cm'3 at a specific pH in the rane 2'2.9 for different samples. !his abrupt increase in h value

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 between pH 2'2.9 reflects the transition from individual molecules to areates of respective

 polymers. Interestinly, the transition in polymer architecture of P1'HBPs was reversible i.e the

areates dissociated into individual molecules when the pH of the medium exceeded 2.9.

However, P19-A9-A-A- (linear rade) displayed hih h value throuhout the rane of solution pH

(uncontrolled areation). Hence branchin units in P1'HBPs definitely stabili&ed the

areates. !he areation behavior of P1'HBPs was further studied usin pyrene as the probe.

Intensity ratio, IAI3 varied from -.4 to 3.- as the pH of the solution chaned from <.- to 1.-

which indicated encapsulation of pyrene to hydrophobic environment of polymer areates,

which developed below certain pH. Gven $G5G" imaes showed that at hih pH, P1'HBPs had

floral structures whereas at low pH they had compact lobular structures (i.e in areate state).

%onclusion

In the first experiment, we were successful in desinin pH responsive HBPs. Fe are further 

tryin to develop hihly water soluble HBP stabili&ed +Ps for #uick and easy sensin of H 1

for waste water treatment.