First, let's address the term "collaborators." When that term is used in Korea, it includes people who worked directly for the Japanese colonial machine but it also includes people who submitted and benefited from the colonial occupation. It's not like Jewish collaborators - capos in the concentration camps and Jews policing themselves in the ghettos and sending others to die. In Korea, it's generally much more subtle since the Japanese were attempting to bring Korea into Japan, not to ethnically cleanse the peninsula. To be sure, some people worked for the Japanese police and military - Park Chung-hee was rumored to have used a false name to hunt down anti-Japanese Korean fighters (in contrast to Kim Il-sung who was an anti-Japanese fighter!) while he was in the Manchukuo army. I say rumored because I just heard about this a few years ago and haven't read the book about it yet. I've heard conflicting information - it's 100% true, it's a rumor, etc - so I'm not sure. But he definitely served in the Manchukuo army, along with other Koreans such as Paik Sun-yup (first full General in the ROK and the guy who saved Park Chung-hee from execution for being a communist!),Chung Il-kwon, and Kim Chang-ryong. Chung was a top general during the Korean War and Kim was a real son of a bitch. He worked for the Japanese ferreting out spies. He then used his counter-intelligence abilities to "clean up" corruption in the ROK military. In reality, he was Syngman Rhee's attack dog and in doing his job, he made a lot of enemies. He was gunned down by his fellow generals in 1956.

But the thing to remember about these people is the jobs that they did. Paik and Chung were simply soldiers doing their job. Paik came from an incredibly poor family and he struggled to become a teacher. On the advice of a friend, he joined the military and found he was good at it and was able to improve his lot in life. People like Park and Kim, however, would have been reviled by the people had they known about it at the time. That's the critical issue. Park was thrown in jail for being a communist and was only freed when Paik spoke up for him. During the Korean War, Paik convinced the US military to train Korean artillery units and he picked Park to be one of the first officers trained as an artillery man. By the end of the war, he had become a Brigadier General and was on his way to becoming a top man in the military with his anti-guerilla activities safely forgotten about.

So back to the question...

The first President of the Republic of Korea was Syngman Rhee. He ruled from 1948 until 1960, when he was ousted in a student uprising over election fraud and his heavy-handed rule. Rhee had been the first President of the Provincial Government in exile (until he was impeached) and he had spent a great deal of time before and after that in the US, pressing the case for Korean independence. He was definitely not a collaborator of any kind. All of his Vice-Presidents had pro-Korean credentials as well.

From 1945 until 1952, Japan was not a sovereign nation and as such, there was no negotiations to be had. But preliminary talks began in October of 1951 between Yang Yu-chan, the Korean ambassador to the US, and Shunichi Matsumoto, the Japanese ambassador to the UK. They met in Tokyo and arranged for the first official talks which began on February 15 and finished on April 25, 1952, three days before Japan regained sovereignty under the Treaty of San Fransisco. The second round of talks began on April 15 and went until the summer. In 1953, Rhee went to Japan to talk to the government. Interesting to note, in this same newspaper on the same day, an article mentions that the Japanese were planning to pay reparations to other countries. Negotiations continued with the third round of talks in October of 53, the fourth round from April of 1958 until 1960, the fifth from October of 1960 until May 15, 1961. The coup that put Park Chung-hee in power happened the next day.

Now you're probably wondering, "why were they negotiating for so long? Why was there a five year gap between rounds 3 and 4?" Simply put, Rhee was anti-Japanese. During the US administration of Japan, the MacArthur line separated the Sea of Japan between Korea and Japan. Korea wanted this line to continue but was told that it was ending with the Treaty of San Fransisco. Rhee then declared the Syngman Rhee line. Any ships that crossed over the line were captured. This resulted in nearly 4000 Japanese fishermen arrested, over 300 ships seized, and over 40 people killed between the lines creation in 1952 and the Japan-Korea Fishery Agreement in 1965. Korea drew the line unilaterally and the Japanese protested but to no avail.

In 1961, after the May 16 coup, the new government pushed ahead with negotiations again in earnest. Kim Jong-pil, Park Chung-hee's right hand man and brother-in-law, gave a series of interviews to the Joongang Ilbo a few years ago. This interview talks about his negotiations. The two governments were stuck over the amount of compensation. In the end, Korea got 800 million dollars in compensation from Japan. They used the money to build the Pohang Steel Company (POSCO), the Guro industrial complex, the Gyeongbu highway, and the Soyang River Dam, all critical pieces in helping the South Korean economy expand.

The final agreement came in 1965 under Park Chung-hee, the former anti-guerilla fighter. The agreement caused a huge backlash as it had been negotiated in secret. Student groups protested but in the end, the Treaty on Basic Relations between Japan and the Republic of Korea was signed, along with the Agreement Between Japan and the Republic of Korea Concerning Fisheries, the Agreement Between Japan and the Republic of Korea Concerning the Legal Status and Treatment of the People of the Republic of Korea Residing in Japan, and the Agreement Between Japan and the Republic of Korea Concerning the Settlement of Problems in Regard to Property and Claims and Economic Cooperation.

So to answer your question, there were no Japanese collaborators in power until Park Chung-hee in 1961. Syngman Rhee's political party had many collaborator supporters, but Rhee was anti-Japanese and he stuck it to Japan when he could. Once Park took over, the Japanese deal came to fruition pretty quickly. Was it because he was pro-Japanese or because Korea needed the money? Probably a little bit of both - the Park cabal knew that they had to get the economy moving and the Japanese money was the quickest way to do that.